CELEBRATING JEWISH NATIONALISM
The Av Harachamim prayer said before Musaf on Shabbos remembers the thousands of martyrs who were murdered al Kiddush HaShem by the Crusades. These Kedoshim accepted the sword of the Crusades rather than accepting their cross.
This prayer, in which we ask HaShem to remember these tzaddikim, is recited every Shabbos before Musaf. On those Shabbosim when we are m’kadesh the chodesh, this prayer is omitted. However, during the Omer it is said even on those Shabbosim. The reason for this is because these tragic events occurred predominantly during the Omer period. In earlier times there were also special Yotzros that were added to Shabbos shacharis commemorating the murder of those kedoshim.